1. Field of the Invention
The present invention relates to a fiber comprising a vinyl alcohol units-containing polymer possessing excellent resistance to hot water and wet heat, and a process for the production thereof. Such fibers are particularly useful as reinforcement for rubber materials, such as tires, hoses, conveyer belts and V belts, and plastics, and for general industrial materials, such as ropes, tents, canvases, fishing nets and other tension materials, as well as for textiles such as clothing and towels having excellent hydrophilic property, soil-resistant property, dyeability and the like.
2. Description of the Prior Art
Fibers from vinyl alcohol units-containing polymers, such as polyvinyl alcohol, have superior strength, elastic modulus, weather resistance, chemical resistance, and adhesiveness compared with polyamide, polyester and polyacrylonitrile fibers and are used in many consumer and industrial products. Wider applications in reinforcing rubber and plastics and general-purpose industrial materials should result from the development of a polyvinyl alcohol fiber having still improved resistance to wet heat and fatigue resistance when used in combination with rubber.
Crosslinking polyvinyl alcohol fiber to improve wet heat resistance is known. Japanese Patent Application Laid-Open No. 120107/1988 proposed acetalization; Japanese Patent Application Laid-Open No. 156517/1989 proposed crosslinking treatment with a peroxide crosslinking agent; Japanese Patent Application Laid-Open No. 207435/1989 proposed treatment with an isocyanate; Japanese Patent Application Laid-open No. 84587/1990 proposed crosslinking with an acid; and Japanese Patent Application Laid-open Nos. 210068/1991 and 249705/1990 proposed crosslinking with a metal compound such as alkoxide or acylate.
According to studies by the present inventors, the above proposed processes require a very high degree of crosslinking to improve wet heat resistance sufficiently. However, such a high degree of crosslinking causes the polyvinyl alcohol to decompose and discolor thereby decreasing fiber strength and elastic modulus. A moderate crosslinking results in a slight decrease in strength and elastic modulus but cannot appreciably improve wet heat resistance.
General-purpose synthetic fibers such as polyester or polyamide fibers are inferior to natural fibers such as cotton and jute in hydrophilic property, soil-resistant property, antistatic property and the like, and have monotonous luster and cool feeling. When dyed, such synthetic fibers are inferior to natural fibers such as wool and silk in the brightness of color, and are difficult to dye in deep colors.
Fibers comprising vinyl alcohol units-containing polymers, in particular ethylene-vinyl alcohol copolymer, have been developed to eliminate the above drawbacks of the general-purpose synthetic fibers.
Ethylene-vinyl alcohol copolymer fibers having hydroxyl groups in the molecule thereof, such as the above-described polyvinyl alcohol fiber, possess superior hydrophilic, anti-soiling and anti-static properties, and dyeability compared with polyester and polyamide fibers. However, such ethylene-vinyl alcohol copolymer fibers possess a low melting point and softening point, have poor resistance to heat and hot water, and are readily damaged by treatments with high-temperature water or steam. For example, treating ethylene-vinyl alcohol copolymer fiber by dyeing at a temperature of at least 100.degree. C., steam or conventional ironing of fabrics comprising ethylene-vinyl alcohol copolymer fiber causes the fibers to soften or stick resulting in the fabric becoming rigid and of poor appearance.
Japanese Patent Publication Nos. 1327/1980 and 5846/1981 proposed improving the above drawbacks of ethylene-vinyl alcohol copolymer fiber by producing composite fiber combining ethylene-vinyl alcohol copolymer with another thermoplastic resin such as polyester, polyamide or polypropylene having better thermal resistance than that of ethylene-vinyl alcohol copolymer. However, when such composite fibers are treated with high-temperature dyeing bath or steam ironing, the ethylene-vinyl alcohol copolymer exposed on the surface of the composite fiber partially softens or sticks. Accordingly, fabrics containing such composite fibers and thus treated are of poor quality because of stiffness, faded luster and poor appearance.
In order to dye fabrics comprising the composite fiber containing ethylene-vinyl alcohol copolymer component without causing the above problems, it is necessary to maintain the dyeing temperature at not more than 90.degree. C. so that no softening or sticking of the copolymer occurs. However, at such a low dyeing temperature, the thermoplastic resin such as polyester or polyamide used for forming the composite fiber cannot be sufficiently dyed causing the composite fiber to be dyed unevenly.